And I think you are in Edge Animate CC(I don't see the new hand and zoom tool in your snapshot ). You can also try to upgrade to Edge Animate CC 2014 and see if you are getting the scrollbars correctly.

I am talking about a behavior of edge (cc or cc 2014) that I discovered, if you set the body of your html file to overflow hidden (in css directly in the html), the scrollbars of the ui stage will disappear. I don't know if it is a bug, but it's definitely a strange behavior :

Explicitly turning off scroll bars on the <body> is fine PROVIDED you have fallbacks for your inner elements to scale/position. If you are using fixed widths/heights you will hit usability issues especially with the variety montors/resolutions.

Why not leave the body tag as is and explore Edge Animate > Stage 100% w/h and or its Responsive Scaling option.